Fuel injectors have enjoyed increasing usage in spark-ignited internal combustion automobile engines over the past several decades and have to a large extent supplanted the carburetor as the means for metering fuel to the engine. In a typical multi-point fuel injection system for a multi-cylinder internal combustion engine, there is one fuel injector per engine cylinder. The fuel injector is poised to inject fuel into the induction air stream for entrainment with combustion air passing to the engine cylinders. Thus, today's typical four-cylinder, six-cylinder, or eight-cylinder engine will be equipped with four, six or eight fuel injectors.
By its nature a fuel injector is a high precision component. The possibility of designing a fuel injector that can be more cost-efficiently manufactured without sacrificing quality and performance merits investigation since, given the size of the global automobile market and the expectation that the usage of fuel injectors will only continue to increase, it is reasonable to anticipate that the market will reward a party who can execute such a design.
The present invention relates to a new and unique fuel injector that is intended to have improved cost effectiveness derived principally from manufacturing considerations. Attention to manufacturing considerations have given rise to a fuel injector in which a number of precision parts are relatively simple in form and only a few parts are more complex. The relatively simple parts, even though they are precision in nature, can be mass produced by established cost-efficient fabrication processes. The relatively more complex parts are obviously more costly to fabricate than the relatively simple ones, but in the aggregate, a more cost-efficient fuel injector results. The parts also provide for the use of more cost-efficient procedures to assemble and adjust the fuel injector. Improvements provided by the fuel injector of the present invention involve features relating both to a number of the individual parts and to cooperative relationships among various parts.
In order to be commercially acceptable, any fuel injector must comply with certain specifications that cannot be compromised. The fuel injector must be capable of accurately and repeatably opening and closing at desired times. When closed, the fuel injector must not leak. The fuel injector must also provide reliable long term performance that remains highly consistent over its useful life.
The present invention is capable of complying with these requirements in a cost effective manner by features relating, inter alia: to a combination valve-armature member that comprises a relatively more magnetically permeable armature element and a harder, relatively less magnetically permeable valve element that are joined together by laser welding; to sealing and landing rings on a flat face of the valve element that is toward a flat face of a circular valve seat member having a central through-hole that is opened and closed by the valve element; to the manner of relating fuel passages through the valve element to these sealing and landing rings; to an annular stop member that comprises a corrugated inner margin for abutment by the valve element to limit displacement of the combination valve-armature member away from the valve seat when the fuel injector in operated open; to the creation of this corrugated margin by an acid etching process; to a skirted orifice disk and the manner of relating it to other internal parts of the fuel injector; to the manner of relating the actuator to the fuel injector; to various internal sealing means; and to methods of assembling various parts of the fuel injector.
The valve seat member is one of the relatively simple parts that can be economically mass produced with precision. It comprises a flat circular disk which has a central through-hole and whose opposite faces are surface finished to a high degree of precision. One of these two surfaces faces the combination valve-armature member, and it is against this surface that the valve element of the combination valve-armature member seats on and unseats from the valve seat member to close and open the central through-hole in the valve seat member. The valve seat member can be very economically fabricated to the requisite precision because of its simple geometry.
Sealing means is provided between the valve element and the valve seat member so that when the fuel injector is closed fuel does not leak from its fuel outlet. This sealing means takes the form of a raised circular sealing ring on the flat surface of the valve element that confronts the flat seating surface of the valve seat member. Since this sealing ring must precisely seal on the flat seating surface of the valve seat member when the fuel injector is closed, the valve element too must be a precision part. In order to maintain precision of the seal over the useful life of the fuel injector, a precision landing ring is also provided in the same surface of the valve element as the sealing ring to engage the valve seat member when the fuel injector is operated closed and thereby react a substantial portion of the closing impact force rather than allowing that force to be reacted solely by the sealing ring. Moreover, the fuel injector must deliver fuel to the area of the valve seat in a way that keeps the sac volume as small as possible, and it must not hydraulically unbalance the combination valve-armature member. (The sac volume is that portion of the internal fuel path which lies downstream of the location where the sealing ring acts.) In order to minimize the sac volume, the diameter and axial dimension of the sealing ring are kept small. In order to maintain satisfactory hydraulic balance on the valve-armature member, fuel passages are provided through it so that when the valve element is closed on the valve seat member pressurized liquid fuel occupies an annular zone intermediate the landing and sealing rings as well as a further annular zone that is radially outwardly of the landing ring. These fuel passageways are diametrically opposite each other, and they intercept the landing ring thereby rendering the latter circumferentially discontinuous while keeping the sealing ring circumferentially continuous. Although certain fabrication costs are concentrated in this combination valve-armature member, overall cost-efficiencies for the fuel injector accrue as a result of efficiencies realized in the fabrication of other parts.
The valve element is circumferentially bounded by a circular spacer ring that is immovably held on the valve body of the fuel injector. This spacer ring can also be cost-efficiently fabricated. The outer circumferential margin of the face of the valve seat member that is toward the valve element serves to hold the spacer ring against a shoulder of the valve body with the stop member being disposed between the spacer ring and the valve body shoulder. The radially inner margin of the stop member radially overlaps the radially outer margin of the face of the valve element that is opposite the face which contains the sealing and landing rings. This radially inner margin of the stop member comprises a corrugated stop face that confronts the valve element. The corrugations are defined by a series of rectangular pockets which are spaced apart side by side in the stop member and that are open both in the axial direction toward the valve element and in the radially inward direction but are otherwise closed by pocket-bounding wall surfaces. This corrugated portion of the stop member is helpful in attenuating the effects of static friction that might otherwise occur if the stop surface were flat and uncorrugated throughout. The stop member corrugations are advantageously formed by an acid etching process. In a modified embodiment, the acid etching process is performed to create a corrugated stop surface comprising a circular annular groove containing small circular buttons uniformly spaced around the groove.
While the valve element is essentially symmetrical about the longitudinal axis of the fuel injector, the armature element is deliberately asymmetrical to provide an unbalanced working gap between the armature element and the stator. As a result, the combination valve-armature member will execute tilting motion away from the valve seat member when the fuel injector is operated open. Furthermore, this tilting motion will occur at the same circumferential location about the combination valve-armature member thereby promoting repeatability of performance which might not be obtainable in a case where an armature is made generally symmetric since such symmetry is apt to result in the tilting motion occurring randomly about the circumference of the combination valve-armature member.
The stop member can be economically fabricated because it is a flat thin ring, and the pockets that form its corrugated surface portion can be created by known acid etching technology. The orifice disk, which is subjacently contiguous the valve seat member, can be economically fabricated by conventional technology. The main valve body and the seat retainer are generally tubular-shaped parts that can be economically fabricated by conventional machining techniques. Because the combination valve-armature member comprises two elements that are other than just simple geometries, more elaborate techniques must be used to fabricate them in any event, and hence the incorporation of a number of structural features into them, such as the landing and sealing rings of the valve element, the fuel passages of the valve-armature member, the shape of the armature element and its joining to the valve element are incorporated to parts which require a number of manufacturing operations anyway; yet an aggregate economy results since the inclusion of such features into parts that already have other than simple geometries yields significant savings in other parts whose geometries can be simplified as a result.
Additional novel features of the invention include: the use of a single O-ring seal to provide three point internal sealing contact with three different parts of the fuel injector; a frustoconical shaped skirt formed in the outer margin of the orifice disk; a conical disk spring washer that resiliently acts between the body of the electric actuator (i.e. the bobbin of the solenoid coil) and a shoulder of the fuel inlet tube that passes through the bobbin to cause the lower flange of the bobbin to forcefully bear against the valve body, while also preventing intrusion of molding material between the fuel inlet tube and the interior of the bobbin when molding material is injected onto assembled component parts of the fuel injector to complete the fabrication by encasing these parts in molded plastic material; and an open sided frame into which the coil assembly is inserted and which, in cooperation with the fuel inlet tube forms a portion of the magnetic circuit for conducting magnetic flux to the armature element of the combination valve-armature member.
A fuel injector fabricated in accordance with principles of the invention is well suited to mass production processes for both metal working and assembly. The fuel injector is also capable of meeting required performance specifications to achieve desired engine operation, keeping in mind fuel economy, exhaust emission requirements and engine performance.
The foregoing, along with additional features, advantages and benefits of the invention, will be seen in the ensuing description and claims which should be considered in conjunction with accompanying drawings. These accompanying drawings disclose a presently preferred embodiment of the invention according to the best mode contemplated at this time for carrying out the invention.